Bacuse left and right - socialism and capitalism - have nothing to do with authoritarianism, which itself is a spurious concept. All systems are authoritarian; you’re not allowed to form a communist state under liberalism, you’re not allowed to form a government under anarchism, etc. You’re forced to play by the rules of the hegemonic system, authoritarian is just a label for whether you personally like those rules.
Bacuse left and right - socialism and capitalism - have nothing to do with authoritarianism, which itself is a spurious concept. All systems are authoritarian; you’re not allowed to form a communist state under liberalism, you’re not allowed to form a government under anarchism, etc. You’re forced to play by the rules of the hegemonic system, authoritarian is just a label for whether you personally like those rules.
Specifically, it was made to separate Hitler from the right and pawn him off to the left.